Heretofore, thermoplastic coated paperboard cartons having flat end closures of the in-folded and/or out-folded fin sealed types formed on opposite ends thereof have been used with generally satisfactory results. However, when the, so-called, in-folded type of end closure is used, several panel thicknesses are operative in the folding operations, the panel thicknesses result in crowding of layers, causing stretching or tensioning of the outermost layers around inner layers to the extent that some outermost layers tend to pull apart and crack, thereby destroying the liquid impermeable thermoplastic layer, producing bulging of the paperboard and subsequent leaking therethrough.